<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Interpret the metazoan phylogenetic tree
  • Describe the types of data that scientists use to construct and revise animal phylogeny
  • List some of the relationships within the modern phylogenetic tree that have been discovered as a result of modern molecular data

Biologists strive to understand the evolutionary history and relationships of members of the animal kingdom, and all of life, for that matter. The study of phylogeny aims to determine the evolutionary relationships between phyla. Currently, most biologists divide the animal kingdom into 35 to 40 phyla. Scientists develop phylogenetic trees, which serve as hypotheses about which species have evolved from which ancestors

Recall that until recently, only morphological characteristics and the fossil record were used to determine phylogenetic relationships among animals. Scientific understanding of the distinctions and hierarchies between anatomical characteristics provided much of this knowledge. Used alone, however, this information can be misleading. Morphological characteristics may evolve multiple times, and independently, through evolutionary history. Analogous characteristics may appear similar between animals, but their underlying evolution may be very different. With the advancement of molecular technologies, modern phylogenetics is now informed by genetic and molecular analyses, in addition to traditional morphological and fossil data. With a growing understanding of genetics, the animal evolutionary tree has changed substantially and continues to change as new DNA and RNA analyses are performed on additional animal species.

Constructing an animal phylogenetic tree

The current understanding of evolutionary relationships between animal, or Metazoa    , phyla begins with the distinction between “true” animals with true differentiated tissues, called Eumetazoa    , and animal phyla that do not have true differentiated tissues (such as the sponges), called Parazoa    . Both Parazoa and Eumetazoa evolved from a common ancestral organism that resembles the modern-day protists called choanoflagellates. These protist cells strongly resemble the sponge choanocyte cells today ( [link] ).

The image on the left shows a choanoflagellate, which is a single-celled protest. The image on the right shows a sponge choanocyte cell that lines in inside of a sponge. The two cells appear identical. Both are egg-shaped with a cone at the back end. A flagellum juts out from the wide part of the cone.
Cells of the protist choanoflagellate resemble sponge choanocyte cells. Beating of choanocyte flagella draws water through the sponge so that nutrients can be extracted and waste removed.

Eumetazoa are subdivided into radially symmetrical animals and bilaterally symmetrical animals, and are thus classified into clade Bilateria or Radiata, respectively. As mentioned earlier, the cnidarians and ctenophores are animal phyla with true radial symmetry. All other Eumetazoa are members of the Bilateria clade. The bilaterally symmetrical animals are further divided into deuterostomes (including chordates and echinoderms) and two distinct clades of protostomes (including ecdysozoans and lophotrochozoans) ( [link] ab). Ecdysozoa    includes nematodes and arthropods; they are so named for a commonly found characteristic among the group: exoskeletal molting (termed ecdysis). Lophotrochozoa    is named for two structural features, each common to certain phyla within the clade. Some lophotrochozoan phyla are characterized by a larval stage called trochophore larvae, and other phyla are characterized by the presence of a feeding structure called a lophophore.

Questions & Answers

Which of the following statements regarding membrane transport is false? 1. Glucose is transported only by facilitated diffusion 2.Each protein carrier will only bind and b transport one type of solute.
#2. Each protein carrier will only bind and b transport one type of soluble
Only
#2 is false for the regarding membrane transport.
Only
Tanks a lot
Thanks a lot
what is gene
Okello Reply
what is somatic cell
garaadmaxamed Reply
what is Biology?
garaadmaxamed
is the study of living things
garaadmaxamed
what is biology
Isiaka Reply
is the study of all living things
Motinga
and their interactions with each other and the environment
Angela
it is the study of all living organisms and their characteristics
ketchem
the study of living things and their surroundings
Ade
what's is biology
Mohamed Reply
what's is dna
Mohamed
deoxybonucliec acid
Gibril
explain the osomor regulations in amoeba and paramecium
Adannaya Reply
explain the osimoregulation in man
Adannaya
who can explain the osmoregulation in amoeba and in man
Adannaya
Hello how are you every body
Sitali Reply
join the conversation
Sitali
l am fine every body
Memiru
I'm very fine_hopefully everyone is fine
Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
hi
Alpha
hi berther
Memiru
hallo
Memiru
what is the meaning of biology
Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
Mabiya Reply
it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
what is DNA
Kashah
what is liver
Hassan Reply
liver is an organ in the body that meterbolise nutrients and produce bile.
Ekechi
what is the function of granum?
Gulfam
what is the faction of liver cancer
Kashah
What is biology
Eric Reply
Biology is you
muayad
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and. evolution
Suzette
biology is the study of living things and none living things
Ekechi
study of living organisms
anji
The mamalian endoskeleton has 206 bones
kaazim Reply
hii
Hannah
hi
Suzette
how you
Hannah
good thanks
Suzette
have you done the actual course?
Suzette
How many bones do human body have?
moses Reply
I don't know please help me
Kisito
206
Waneh
206
Moses
206
anji
what are these geneti materials
ONELIA Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask